The purpose of the proposed investigation is to provide a systematic and comprehensive evaluation of behavioral, physiologic and anatomic measures in normal aging and Alzheimer's disease. A longitudinal study will help in evaluating the effects of NA and SDAT on progression of intellectual decline as it relates to changes in regional brain anatomy and physiology. Neuropathological evaluations will be obtained and correlated with the in vivo measures. We propose to study 60 normals and 60 patients with SDAT over a course of three years. Subjects admitted into the protocol will undergo standardized behavioral evaluation of cognitive affective and daily functioning. These will be repeated at specific intervals. Regional cerebral blood flow will be measured using the 133-Xenon inhalation method, during resting and solving memory tasks. Atrophy will be assessed using automated magnetic resonance imaging analysis. The behavioral, physiologic and anatomic measures will be integrated using multivariate statistical methods and topographic analysis. Data obtained will contribute to the understanding of the process of normal aging, the course of SDAT and their relation with pathologic findings. This may eventually lead to a better understanding of regional brain function in NA and SDAT and ultimately to the development of early detection.